In rectangular balers bales are formed by compressing crop material in a bale chamber by a plunger that reciprocates in the bale chamber.
An example of a bale chamber of the prior art is shown in FIG. 1. The bale chamber 1 comprises a top wall 2, a bottom wall 5, and two side walls 6. At one end of the bale chamber there is provided a plunger 3. The top wall 2 and/or the bottom wall 5 and/or the side walls 6 may be provided with a series of hay dogs 4. When the plunger moves in a discharge direction F to add a flake of crop to the bale, the hay dogs 4 hold the flake in shape. The top wall 2 and the side walls 6 are typically hinged at the end near the plunger 3, allowing to adjust the position thereof, and to exert a compacting force on the top wall and the side walls. In that way the density of the bales may be regulated.
The problem with the balers of the prior art is that in certain circumstances it is not possible to produce bales with an acceptable density, even when using the maximum pressure on the walls of the bale chamber.